1. Field of the Invention
The present invention relates to apparatus for examining a particular miniature pattern formed on a substrate to detect any defect contained in the pattern. More particularly, the present invention relates to a pattern examining apparatus in which the pattern transcribed onto a mask or reticle in the manufacturing process of integrated circuit (IC) is compared with the design data for forming the pattern to examine it whether or not the pattern has correctly been transcribed.
2. Description of Prior Art
For the above-mentioned type of pattern examining apparatus hitherto known there have been employed various comparing examination methods
One of the known methods is the so-called chip comparison method according to which chips having the same patterns formed on the same mask are compared with each other.
Another well-known method is the so-called data comparison method. According to the method, design data are developed on an image memory as a bit pattern which is then compared with the image data obtained from the real pattern on the mask or reticle. The comparison is carried out picture element by picture element.
However, these known examination methods some drawbacks.
In the case of chip comparison method, if every chip has the same defect (common pattern defect), it is no longer possible to detect the defect. Further, the chip comparison method can not be used to examine a reticle pattern used as an original for making masks. This is because in many cases such reticle pattern exists alone.
As compared with the chip comparison method, the latter mentioned data comparison method has the advantages that it enables to detect even the common defect to chips and that it can be used also to examine the reticle pattern. The reason for this is that according to the data comparison method, the real image is compared with the corresponding design data. However, this data comparison method also involves some difficult problems. The problems are mainly attributable to the fact that a great deal of data must be stored in the image memory after converting the design data into image data of the individual picture elements. Thus, the image memory is required to have a very large capacity. The time required for input-output of the data to and from a computer becomes too long to be acceptable. Furthermore, it renders the examining apparatus large and complicate.